1. Field of the Invention
The present invention relates to guidance systems for missiles or the like, and more particularly, to a means and method of coding a light beam projected from a missile firing position toward a target and received by a missile fired toward the target.
2. Description of the Prior Art
Beam rider missiles are known today which are guided by a laser beam pointed from a missile launching site to a target. The beam contains modulation signals which appear at a receiver in the missile and are decoded to form guidance commands for directing the missile basically along the centerline of the beam to intercept the target. U.S. Pat. No. 4,014,482 to Esker et al is one which discloses a rotating light chopper or reticle with opaque and transparent portions for coding or modulating the beam. The center of the reticle rotates around the center of the generated beam, with only a portion of the reticle intersecting the beam at any one time. The laser beam is pulsed at two different rates and coordinated with the reticle position to provide the missile receiver with magnitude and phase components to use in determining the missile position with respect to the beam centerline.
U.S. Pat. No. 3,957,377 to Hutchinson shows a similar system wherein a rotating reticle or disc comprises two separate patterns for providing yaw and pitch position data in the guided body, as respective portions of the reticle pass across the beam.
U.S. Pat. No. 3,711,046 to Barhydt et al discloses a missile guidance system wherein a source of infrared radiation at the missile produces a beam detected by a guidance unit at the sight position. A rotating reticle in the guidance unit has concentric bands of different width as the bands progress around the reticle, producing a sinusoidal modulation of the infrared image intercepted thereby.
Other prior art systems use various rotating disc patterns in target tracking applications. The U.S. Pat. No. 3,500,415 to Bishop and U.S. Pat. No. 3,002,097 to Nuut are examples of such. U.S. Pat. No. 2,931,912 to Macleish uses a scanning disk pattern which provides two signals indicating, respectively, the polar coordinates of the target.
These known systems are all relatively complicated and it is an object of the present invention to provide a guidance method for a beam riding missile or the like which is simpler than conventional methods. Another object is to provide, in a guidance system, a novel beam projection and coding means.